The invention relates to a device for and and a method of working up used pickling and etching liquids.
Many chemical and electrochemical methods of etching and pickling metals are in use in which a metal object is subjected to a surface treatment or in which it is subjected to a non-mechanical metal-removing treatment. In all these methods metal goes into solution. Especially in continuous processes in which recirculation takes place the gradual increase in concentration of ions or the formation of a precipate may considerably disturb or even stop the desired etching or pickling reaction. However, continuous regeneration is not always easy to perform so that in many processes large quantities of consumed liquids remain which as a rule cannot be disposed of as such in view of encironmental pollution and the value of the dissolved substances. Much is known already about the recovery of the metal gone into solution and the used etching and pickling agent, respectively. Much is known in particular about liquids in which a volatile acid or a salt of a volatile acid is present as a reagent.
A device for and a method of recovering hydrochloric acid and iron in the form of iron oxide is known from U.S. Pat. No. 2,471,844.
The device employed comprises a cylindrical reaction space which is accomodated at an angle with respect to the earth's surface and is filled with balls which can traverse through the reaction space, means for supplying the said liquids to the reaction space, means for treating the balls to a temperature at which at their surface the substances formed during etching and pickling, respectively, and present in the liquid to be worked up can undergo a pyrolysis reaction and the solvent evaporates, mechanical means for removing pyrolysis products present on the surface of the balls after the balls have left the reaction space, and means to process the released gases and vapours.
The means for heating the balls are embodied in the said U.S. Patent in a vertical furnace in which the balls of an inert material are introduced at the top, are heated at a temperature of, for example 1000.degree. C. and are removed at a lower level and moved into a rotary kiln the axis of which encloses a small angle with the earth's surface and in which the iron chloride-containing liquids are also supplied. A reaction takes place at the surface of the balls with gases in which iron oxide is formed and hydrochloric acid in gaseous form escapes. If the liquid comprises iron in the trivalent form ferric oxide is deposited on the balls. However, if it comprises iron in the bivalent form oxygen must be added to the rotating furnace if ferric oxide is desired. The balls covered with iron oxide fall on a grate as a result of which the iron oxide thereof is removed. The balls are returned to the vertical oven. The escaping gases are applied to an absorption tower and thus converted into a hydrochloric solution of the desired strength. Ferric nitrate solutions and aluminium chloride solutions are worked up in a similar manner.
A disadvantage of the known device is that the rotary furnace in which the reaction with the agressive gases takes place involves great sealing problems.